[libcxx] Build with -fvisibility-inlines-hidden -- Remove 20 inline definitions from the dylib

[EricWF]

Summary

This patch turns on -fvisibility-inlines-hidden when building the dylib. This is important so that libc++.dylib doesn't accidentally export inline-functions which are ODR used somewhere in the dylib.

On OS X this change has no effect on the current ABI of the dylib. Unfortunately on Linux there are already ~20 inline functions which are unintentionally exported by the dylib. Almost all of these are implicitly generated destructors. I believe removing these function definitions is safe because every "linkage unit" which uses these functions has its own definition, and therefore shouldn't be dependent on libc++.dylib to provide them.

Also could a FreeBSD maintainer comment on the ABI compatibility of this patch?

[EricWF]

I just spoke with Jonathan Wakely about this change, and he believes that it should be ABI safe.

[emaste]

lib/abi/CHANGELOG.TXT

22 ↗

(On Diff #74618)

Should we also include in this comment the further justification from your Phabricator description above (about having own definitions)?

[dim]

LGTM.

[EricWF]

• Address review comments by adding better documentation in the CHANGELOG.TXT.

libcxx/trunk/CMakeLists.txt

 endif()
 
 # On all systems the system c++ standard library headers need to be excluded.
 # MSVC only has -X, which disables all default includes; including the crt.
 # Thus, we do nothing and hope we don't accidentally include any of the C++
 # headers
 add_compile_flags_if_supported(-nostdinc++)
 
+# Hide all inline function definitions which have not explicitly been marked
+# visible. This prevents new definitions for inline functions from appearing in
+# the dylib when get ODR used by another function.
+add_compile_flags_if_supported(-fvisibility-inlines-hidden)
+
 # Let the library headers know they are currently being used to build the
 # library.
 add_definitions(-D_LIBCPP_BUILDING_LIBRARY)
 
 # Warning flags ===============================================================
 add_definitions(-D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 add_compile_flags_if_supported(
     -Wall -Wextra -W -Wwrite-strings

libcxx/trunk/lib/abi/CHANGELOG.TXT

 Afterwards the ABI list should be updated to include the new changes.
 
 New entries should be added directly below the "Version" header.
 
 -----------
 Version 4.0
 -----------
 
+
+* rTBD - Add -fvisibility-inlines-hidden when building libc++.
+
+  Although this change removes symbols, it should still be non-ABI breaking
+  since all of the definitions removed are inline functions. For this reason
+  removing these symbols is safe because every "linkage unit" which uses these
+  functions will contain their own definition.
+
+  x86_64-linux-gnu
+  ----------------
+  SYMBOL REMOVED: _ZNSt12bad_any_castD0Ev
+  SYMBOL REMOVED: _ZNSt12experimental15fundamentals_v112bad_any_castD0Ev
+  SYMBOL REMOVED: _ZNSt3__114__codecvt_utf8IDiED0Ev
+  SYMBOL REMOVED: _ZNSt3__114__codecvt_utf8IDsED0Ev
+  SYMBOL REMOVED: _ZNSt3__114__codecvt_utf8IwED0Ev
+  SYMBOL REMOVED: _ZNSt3__115__codecvt_utf16IDiLb0EED0Ev
+  SYMBOL REMOVED: _ZNSt3__115__codecvt_utf16IDiLb1EED0Ev
+  SYMBOL REMOVED: _ZNSt3__115__codecvt_utf16IDsLb0EED0Ev
+  SYMBOL REMOVED: _ZNSt3__115__codecvt_utf16IDsLb1EED0Ev
+  SYMBOL REMOVED: _ZNSt3__115__codecvt_utf16IwLb0EED0Ev
+  SYMBOL REMOVED: _ZNSt3__115__codecvt_utf16IwLb1EED0Ev
+  SYMBOL REMOVED: _ZNSt3__117__assoc_sub_stateD0Ev
+  SYMBOL REMOVED: _ZNSt3__117__assoc_sub_stateD2Ev
+  SYMBOL REMOVED: _ZNSt3__117__libcpp_sscanf_lEPKcP15__locale_structS1_z
+  SYMBOL REMOVED: _ZNSt3__119__libcpp_asprintf_lEPPcP15__locale_structPKcz
+  SYMBOL REMOVED: _ZNSt3__119__libcpp_snprintf_lEPcmP15__locale_structPKcz
+  SYMBOL REMOVED: _ZNSt3__120__codecvt_utf8_utf16IDiED0Ev
+  SYMBOL REMOVED: _ZNSt3__120__codecvt_utf8_utf16IDsED0Ev
+  SYMBOL REMOVED: _ZNSt3__120__codecvt_utf8_utf16IwED0Ev
+
+  x86_64-apple-darwin16.0
+  -----------------------
+  No Changes - inline symbols are already hidden
+
+
 * r284206 - Implement C++17 aligned allocation in <new>
 
   x86_64-linux-gnu
   ----------------
   Symbol added: posix_memalign@GLIBC_2.2.5
   Symbol added: _ZdaPvSt11align_val_t
   Symbol added: _ZdlPvSt11align_val_t
   Symbol added: _ZnamSt11align_val_t

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